In operating such an extrusion apparatus, the parts defining said passageway adjacent said outlet end thereof suffer very great working loads and very high operating temperatures. Of such highly stressed (mechanically and thermally) parts, those that suffer greatest wear or damage are the stationary, feedstock-engaging parts of, or associated with, said stationary shoe member, particularly on said abutment member, said die member and the stationary parts that support those items.
For the convenience of readily making good worn or damaged surfaces or parts, the abutment member, and the die member and its supporting parts are made as separate replaceable items which are rigidly but removably secured in the stationary shoe member.
In order to reduce the temperatures at which those replaceable items operate, such items have been provided with internal cooling passages through which cooling water has been circulated. However, such cooling measures have not been very effective, for the reasons that
(a) the small sizes of those items and the high mechanical loads to which they are subjected have severely restricted both the sizes of the internal cooling passages and their proximity to the source of heat, so that the cooling water has been unable to extract heat at an adequate rate, and
(b) the materials used for such small items (e.g. high-speed tool steels) have relatively poor heat transmission properties.
As a consequence of the low dissipation of heat by the cooling water, plastic flow of the tip of the abutment member, at its free end adjoining the bottom of the groove in the wheel member, has been experienced, due to the excessive tip temperatures reached. This has severely limited the life of the abutment member, and the running time of the apparatus between successive occasions when the abutment member has to be replaced. This in turn has led to a reduction in the quantity of the output extrusion product produced, due to the down-time during which the apparatus cannot be operated.
Also, with prolonged use, there has been the risk that the extrusion die may overheat to a temperature at which its mechanical strength is impaired, with the consequent risk of deformation and/or increased wear of the die.
After experimentation with various different arrangements of internal cooling passages, particularly in the abutment member, highly satisfactory results have now been achieved by means of an entirely different arrangement for cooling the abutment member. Such different arrangement, and various modifications thereof, have been described and claimed in the copending, parent patent application No. 574,511, filed Jan. 27, 1984, now U.S. Pat. No. 4,610,725, from which application this present application has been divided.
The use of the invention of that parent application enables such a rotary, friction-type, continuous extrusion apparatus to operate at lower temperatures, for longer periods of time, and with longer operating lives for those parts of the apparatus that are subjected to high mechanical and thermal stresses.
The beneficial results obtained by the use of that invention can be enhanced by the use in conjunction therewith of the invention of this divisional application.
By way of introduction to the present invention, reference should be made to the passage in the specification of that parent application, which begins--"It is believed that the highly beneficial ..." and ends--"... at which heat will be conveyed to the cooling zone by the wheel member."
That passage appears later in this specification, since the description given later with reference to the drawing figures is the same as that given in said parent application.